The present invention relates to apparatus and method of growing cells in vitro, particularly mammalian cells.
U.S. Pat. No. 3,883,393 and U.S. Pat. No. 4,220,725, both issued to Knazek et al, describe apparatus and methods for maintaining and growing mammalian cells in vitro. The apparatus disclosed by Knazek et al includes a cartridge of semipermeable tubular members, more specifically, semipermeable hollow fibers. In the methods disclosed by Knazek et al, cells suspended in a nutrient medium are introduced into the shell side of the bioreactor and allowed to settle on the hollow fibers which they refer to as "capillaries." A nutrient medium is continuously circulated through the tube side of the bioreactor to nourish the cells contained therein and thereby promote growth. The waste products of the growing cells were allowed to accumulate within the recirculating "perfusion medium" and that "perfusion medium" was disposed of and replaced by fresh nutrient medium everyday or every other day. The changing of the nutrient medium was necessary in order to prevent substances toxic to the cells, e.g. lactate, from reaching a level which would kill or deplete the cell culture. Knazek et al included a stirred reservoir or hold tank within their loop as a convenient method for adding and withdrawing the liquid nutrient medium on alternating days or on a daily basis. Accordingly, Knazek et al adopted the conventional approach to the culturing of mammalian cells which is essentially a batch process with respect to the replacement of the nutrient medium.
"VITAFIBER.RTM. II/Plus" is considered an improvement over the apparatus and method of Knazek et al in that it enables operation with replenishment of the nutrient liquid on a continuous basis, rather than in a batch manner. Nutrient and waste levels in the recirculating liquid medium can be better controlled. This enhanced controlability is particularly important in the culturing of cells which are very sensitive with respect to lactate levels. Provision is made for automatic pH control by addition of acid or base. However, no provision is made for automatic control of nutrients and the system is subject to nutrient depletion.
In these prior art systems, lactate level was monitored by addition of a pH color indicator, e.g. phenol red, to the liquid medium. It has also been conventional in this art to monitor lactate levels by periodically withdrawing samples from the liquid medium and analyzing for lactate using a conventional lactate analyzer